In the art of MOS (metal-oxide-semiconductor) integrated circuits, many types of such circuits require an input clock signal, that is, a periodic sequence of electrical pulses, in order to provide a means for the proper timing of various electrical circuit functions. Among such types of MOS circuits that require such timing are the semiconductor charge coupled devices (CCD) and synchronous logic circuit devices such as the microprocessor. In many of these cases it is desirable to have a means for detecting clock interruption, that is, when the input clock stops (is "stuck"), at its high, low, or any intermediate voltage level.